This invention relates to a pultruded part and to a method of pultrusion.
Pultrusion is a well known and commonly used technique for forming continuous parts of constant transverse cross-section in which the parts are formed from a set resin material reinforced by longitudinally continuous fibre reinforcement elements.
Generally, although not essentially, the resin material is formed from a thermo-setting resin. The fibre reinforcement elements carrying the resin are passed into a die which forms the resin in liquid form and the fibre reinforcement into the required shape defining the transverse cross-section. After shaping in the die, a heating process is applied to the materials in the die so as to effect thermo setting of the resin material. The part thus emerges from the die in a set condition so that a pulling force can be applied to the part downstream of the die and this pulling force provides the necessary forces for drawing the longitudinally continuous fibrous reinforcement elements through the section in which the resin is applied and into the die. Generally the resin is applied simply by dipping the fibers through a bath of the resin.
The part can be formed simply from rovings which are longitudinally continuous individual fibers formed into a bundle or can include rovings and also a mat structure which is inserted with the rovings into the die. However, in both cases the materials are generally soaked with the resin material prior to entry into the die so the die acts to squeeze the resin material throughout the fibers to ensure an intimate mixture between the fibers and the resin.
In most cases the amount of fiber is of the order of 60 to 70% of the total part so that the resin material is of the order of 30 to 40%. In some oases filler materials can be added.
Different resin materials are available for achieving different effects. In general terms the resins include polyester, vinylester, acrylic materials and epoxy, all of which can be provided in a form which is thermo-setting. It is well known that polyester is currently the cheapest of the available resins but has the disadvantage that it is weak relative to the other resins and thus has a tendency to crack or split when a force is applied to the finished part in a direction transverse to the length of the part. In order to control the economics of the finished product, therefore, it is necessary to make a careful selection of the resin material in relation to the thickness of the part and therefore the quantity of the resin material so that the part is properly designed to achieve the required properties at a required price. It is generally known, therefore, that one of the available resins can be selected and the thickness of the part then controlled to provide the required characteristics.
It is one object of the present invention to provide an improved pultruded part and an improved method for pultrusion which enables the manufacture of a part of the required strength at a reduced price.
According to the first aspect of the invention there is provided a pultruded part comprising an integral part body having a constant cross-section transverse to a longitudinal direction of the body, the body being formed from set resin material having embedded therein fibre reinforciing elements at least some of which are continuous in the longitudinal direction of the body, the body including at one portion of the cross section a first resin material and at a second distinct portion of the cross section a second resin material different from the first resin material, each of said first and second resin materials exending continuously longitudinally of the body and having some of said fibre reinforcing elements embedded therein.
According to a second aspect of the invention there is provided a method of forming a pultruded part comprising an integral body having a constant transverse cross-section, the method comprising providing a plurality of longitudinally continuous fibre reinforcement elements, applying to said elements in liquid form settable resin material, passing the elements and the resin material applied thereto through a die to form the elements and the resin material into a shape defining said transverse cross section and causing the resin material to set in said shape, wherein saie of the fibre reinforcement elements have applied thereto a first resin material and others of the fibre reinforcement elements have applied thereto a second resin material different from the first resin material.
One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: